Physiologic jaundice occurs when bilirubin, a breakdown product of the red blood cells, is not detoxified at the appropriate rate. Bilirubin levels in preterm infants are often elevated. This can result in damage to various parts of the brain and can consequently affect a range of behaviors. In this study we wished to determine if the subtle impairment in sensory, neurological, and affective function of low risk preterm infants is associated with physiologic jaundice. Bilirubin to protein levels in the blood of 45 low risk black preterm infants were correlated with four measures of tactile, auditory, and visual information processing, with performance on the Parmelee Neurological Examination, with observed activity level, with observed state and state-change, with length of observed crying and fussing, with two measures of ease of soothing and with judgements of acoustic features of the infants' cries. Of the 24 behavioral measures, 6 correlated significantly with the bilirubin to protein levels. Bilirubin to protein levels were associated with more time spent asleep and with a slower responsiveness to a visual stimulus. The pattern of the results did not change when either the effects of length of phototherapy (a treatment for jaundice) or the effect of other medical risks were statistically removed. The findings raise questions about the specific mechanisms through which bilirubin affects later visual responsiveness adn state regulation in preterms (e.g. destruction of brain cells, degradation of myelin sheath, changes in neurotransmitters?). Likewise, the findings raise questions about the timing of phototherapy (preventive vs. responsive phototherapy) in the treatment of young preterm infants.